1. Field of the Invention
The present invention relates to an image processing technique for processing tomograms.
2. Description of the Related Art
Conventionally, ophthalmic examinations have been made for the purpose of earlier diagnoses of diseases that come before lifestyle-related diseases and causes of blindness. In general, in such ophthalmic examinations, an ophthalmic tomography apparatus such as an OCT (Optical Coherence Tomography) is used. When such ophthalmic tomography apparatus is used, since it allows to three-dimensionally observe the state of the interior of retina layers, more accurate diagnoses can be given.
Tomograms captured using the ophthalmic tomography apparatus normally undergo image processing in a computer to detect the boundaries of respective layers and blood vessels of a retina, and tissue forms such as the forms of the layers and those of blood vessels are then measured. FIG. 14 shows states in which the boundaries of the layers and blood vessels are detected and tissue forms of an eye portion are measured in various tomograms captured using the ophthalmic tomography apparatus.
An example of 14a of FIG. 14 shows a state in which after an inner limiting membrane B1, inner plexiform layer boundary B4, boundary B5 between inner and outer photoreceptor segments, and retinal pigment epithelium boundary B6 are detected, a retina thickness T1 and GCC (Ganglion Cell Complex) thickness T2 are measured. An example of 14c of FIG. 14 shows a state in which after retinal blood vessels V are detected, the diameters of the retinal blood vessels V are measured.
In this manner, by measuring tissue forms of an eye portion, and comparing whether or not the measurement results (the retina thickness T1, the GCC thickness T2, the diameters of the retinal blood vessels V, and the like) fall within normal value ranges, abnormalities (that is, morbid portions) can be detected.
In some diseases of an eye portion, morbid portions which mutually have deep relevance (primary and associated morbid portions) may separately exist in a plurality of layers. In case of such disease, it is also important to recognize the relevance (distances between the primary and associated morbid portions, the presence/absence and sizes of the associated morbid portions, etc.) between the morbid portions at the time of a diagnosis or treatment plan.
For example, diabetic retinopathy will be described below. 14b of FIG. 14 shows an ophthalmic tomogram of a patient who suffers diabetic retinopathy. As shown in 14b of FIG. 14, in case of diabetic retinopathy, capillaries of retinal blood vessels in retina inner layers become hypertrophic to form microaneurysms MAi (i=1, . . . , n1). Also, some microaneurysms MAi leak plasma components, which are accumulated in retina outer layers. In general, exudasive morbid portions formed by accumulating the plasma components in a massive form are called cysts Cj (j=1, . . . , n2).
In case of diabetic retinopathy having such morbid portions, in a treatment, the microaneurysms MAi (primary morbid portions) from which plasma components have leaked out are specified, and are irradiated with a laser beam, thus stopping leakage. At this time, in the vicinity of the microaneurysms MAi from which plasma components have leaked out, associated cysts Cj are often formed, as shown in 14b of FIG. 14, and the leakages of plasma components can be recognized by measuring the sizes of the associated cysts Cj (associated morbid portions).
Therefore, a microaneurysm MAi having a larger cyst Cj at its neighboring position is a primary morbid portion which has a high necessity level of a laser therapy in a treatment plan. However, a portion which has a serious influence on a visual acuity (central fovea F1) and that which has a serious influence on optic nerves (optic papilla) cannot be irradiated with a laser beam. For this reason, upon planning a laser therapy, distances between these portions and leaking points have to be measured so as to confirm whether or not the leaking points are sufficiently separated from these portions.
That is, upon displaying a tomogram, the sizes and positions of the cysts Cj, and the distances between the cysts Cj and the microaneurysms MAi, central fovea F1, and optic papilla can be recognized at a glance, thus expecting to improve the convenience at the time of a diagnosis and treatment plan.
As described above, it is desirable to display the processing result obtained by executing image processing of tomograms captured using the ophthalmic tomography apparatus, so as to allow an operator to easily recognize the relevance of morbid portions for each disease.
On the other hand, various methods for displaying morbid portions detected by executing image processing of tomograms captured using an ophthalmic tomography apparatus have been conventionally proposed.
For example, the specification of U.S. Pat. No. 7,505,142 discloses an arrangement which generates a single projection image by limiting to some layers in a retina, and highlights a retinal blood vessel. Also, Japanese Patent Laid-Open No. 2009-89792 discloses an arrangement which compares and displays form abnormalities (thinning) at a plurality of points along a direction in which a retina nerve fiber travels.
However, the arrangement described in the specification of U.S. Pat. No. 7,505,142 generates a single projection image in some layers, and that described in Japanese Patent Laid-Open No. 2009-89792 displays a single layer. That is, these arrangements do not display morbid portions which separately exist in a plurality of layers in consideration of their relevance, and display modes of these arrangements are not suited to give a diagnosis or make a treatment plan for morbid portions for which their relevance across a plurality of layers has to be recognized.